Gas pressure regulators have a number of uses. One such use of a gas pressure regulator includes providing a fixed output pressure from a variable high pressure inlet source. For example, a high pressure tank of breathing gas at 3000 psi may provide an output gas at 20 psi to a downstream device. However, one of the shortcomings of the prior art gas pressure regulators is that, as the high pressure source is depleted, the low pressure, even when set at a fixed value, may rise above that value before the regulated valve shuts off the source. For example, as a high, variable pressure source gas initially at 3000 psi drops, through use, say to 800 psi, the initial set pressure for closure at the transition or regulated valve can rise from its initial set pressure of, for example, 20 psi, to a higher pressure of, for example, 38 psi.
While in some applications this may not be a problem, other applications are sensitive to over pressurization from an initial set pressure. Therefore, there is a need for a gas pressure regulator in which the set pressure at the outlet port or in a regulated gas chamber does not change materially with the drop in pressure of the high pressure gas.
Changeover valves are known in the prior art where a pair of high pressure gas sources feed a single device, which provides a regulated downstream pressure. Typically, one of the pair of high pressure gas sources provides pressure to the device and, when it is at or near depletion, a second high pressure gas source begins to provide regulated gas downstream of the device. That is to say, there are devices that provide a pair of high pressure gas sources to a single device to regulate the downstream flow thereof, and which devices may selectively choose one or the other of the high pressure gas sources to which it is engaged. This provides the utility of an easy switchover from one gas source to the other when one of them runs low.